Hello Scotty, I have a 2006 Honda Civic Si, 6-Speed manual with 133,266 miles. When I’m in 6th gear I notice a rattling sound, and it sounds metallic, only when I’m full throttle and not going the speed you should be in 6th. IE: if I’m going maybe 40mph and The more throttle the louder the rattle in 6th I hear. Goes away if going appropriate speed in 6th. tested other gears and can’t hear it maybe the engine sound covers it up, (doesn’t happen if I rev in neutral). Please help I can upload a video if needed. No OBD codes.
It is a normal thing in manual transmission. You should get to high enough rev and then change gear, although it won't hurt the engine but it doing that results in the rattle you have.
You need to be in the correct rpm for the gear your in. Downshift... and imo, loading the engine improper at low rpm's isn't a good idea for longevity of the engine and increases blowby among other things.
Sounds like classic engine spark knock. What type of fuel are you using? Premium?
Also, it sounds as you lugging your engine, … heavy foot at low RPM! And so, just perhaps, it’s time to bone up on how to properly drive with a manual transmission? Dunno, … but please, elaborate on your driving style and habit a bit more.
Anyway, so you know, lugging the engine is a very, very bad idea! So stop it before your engine fails, …
F.S.
